The invention relates in general to microelectromechanical systems (MEMS) type optical switches and in particular to a MEMS optical switch using a thermal actuator.
Optical MEMS is a fairly new subject with many switch designs appearing in the past 5-6 years. Most MEMS optical switches work by actuating a slider in and out of the optical path between one or several input and output optical fibers. The slider acts in one of two ways. First, it could serve to block the light from entering the output optical fiber. Second, the slider could contain a reflector the redirects the light to the output fiber. Due to design and fabrication limitations, these switches are often very optically inefficient.
Many of these limitations can be overcome by directly actuating the input and/or output optical fibers in and out of line with each other to make for more efficient optical transfer. The major advantage of the moving fiber type optical switch is that the optical efficiency is greater than the moving reflector type switches. The surfaces used for micro-optical mirrors often are not very reflective and the input and output fibers must be placed at great distances from the reflector surface which further increases losses.
U.S. Patent Publication 2002/0102061 ('061) discloses an optical switch that is fabricated on a substrate and switches planar waveguides into and out of alignment with each other. A heat source (such as electrical resistance heating) may be used to provide heat to the movable structure. The heat causes thermal expansion of the movable structure and resulting movement of the waveguide into or out of alignment with another waveguide.
The '061 device uses waveguides. In general, optical fibers are more optically efficient than fabricated waveguides, optical fibers are cheaper to make than fabricated waveguides and optical fibers (larger diameter) can carry more power than waveguides. Also, in the '061 device, the movable waveguide is integrated into the thermal actuator. Because optical properties of materials are temperature dependent, the waveguides of the '061 device may be adversely affected by temperature increases in the thermal actuator.